80 TERRESTRIAL MAGNETISM. 



tions of Captain Lefroy : Phil. Trans. 1846, Pt. in. 

 p. 237336. 11. On the periodic laws of the disturb- 

 ances of the declination (magnetic storms) at Toronto in 

 Canada, and at Hobarton in Van Diemen Island, and on 

 the accordance of the approximately decennial period of the 

 magnetic variations depending on the sun, with the also 

 approximately decennial period, discovered by Schwabe of 

 Dessau, in the phenomena of the solar spots : Phil. Trans. 

 1852, Pt. i. p. 121124. 



1839. Isoclinal and isodynamic lines in the British 

 Islands, from observations of Humphry Lloyd, John 

 Phillips, Robert Were Eox, James Eoss, and Edward 

 Sabine. In 1833, the British Association, at Cambridge, 

 pointed out the importance of systematic observations of 

 the inclination and force being made in different parts of 

 the kingdom; and already, in the summer of 1834, their 

 wish had begun to be fulfilled by Professor Lloyd and 

 Colonel Sabine; in 1835 and 1836 the work was extended 

 to Wales and Scotland, and in 1838 complete isoclinal and 

 isodynamic maps of the British Islands were presented to 

 the British Association, and published in the Report of the 

 Meeting at Newcastle, p. 49 196. 



18381843. The important voyages of Sir James Clark 

 R/oss towards the South . Pole, equally admirable for the 

 knowledge gained thereby of the existence of the much- 

 doubted Antarctic lands, and for the new light thrown on 

 the magnetic condition of very -large and important portions 

 of the earth's surface. The numerical values of the three 

 elements of terrestrial magnetism were determined over 

 almost two-thirds of the area of the higher latitudes of the 

 Southern hemisphere. Sir James Ross's magnetic obser- 



